The Carter administration was denounced in a Senate subcommittee yesterday for waiting until the Soviet Union Invaded Afghanistan before cracking down on high-technology exports that the Russians have diverted to military use.

Sens. Henry M. Jackson (D-Wash.), Sam Nunn (D-Ga.) and William S. Cohen (R-Maine) also questioned whether the administration is cracking down enough now, even though a high Pentagon official said it has learned from what he called "the errors" of the past.

Jackson said he was skeptical of "born-again hawks" and "retroactive righteousness," and Nunn sarcastically suggested that the administration sees nothing wrong with helping the Soviets build military equipment "as long as it's just sitting there pointing at us . . . It's all right until they invade with it."

Two focal points of the 4 1/2-hour hearing by the Senate Governmental Affairs investigations subcommittee were the Soviets' Kama River truck factory and the Zil Factory and laboratory, both of which have been licensed to import U.S. computers and other sophisticated equipment.

The Pentagon says Kama trucks turned up in Afghanistan, and Zil reportedly is producing missile launchers.

The United States had at least "fragmentary" indications in 1977 that Kama was producing trucks for the Soviet army, but lacked conclusive evidence until late 1979, according to William J. Perry, undersecretary of defense for research and engineering.

After the Soviets moved Kama trucks into Afghanistan, two Kama export licenses were revoked as part of a U.S. crackdown on high-technology exports to the Soviet Union pending a general Carter administration review of export licensing policies.

Subcommittee members wanted to know why it took three years to stop shipments to Kama and why Zil's licenses weren't revoked after the Afghanistan invasion. Panel members did not appear satisfied with the answer from the Commerce Department, which regulates trade with communist countries.

Homer Moyer, the department's general counsel, said use of Kama trucks for military purposes did not technically violate a 1971 license granted, he noted, by the Nixon administration. When shipments were stopped, it was done on national security grounds, he added. Moyer said the difference between the Kama and Zil cases was that Kama equipment was actually involved in the invasion.

At this point, Jackson accused the department of presenting a "miserable case" backed up by "fallacious reasoning." Cohen objected that Zil was more objectionable than Kama. Nunn chimed in, saying, "That's a sad state of affairs. It means this country cannot be awakened short of Soviet intervention . . . at least not this administration."

No one present attempted to defend the wisdom of earlier policies, and Jackson as well as administration officials took pains to note that the policies went back at least three administrations.

"I think we made some errors in judgment," said Perry, although he said the Pentagon did not agree with those in the administration who thought it was "worth taking the risks" to promote detente by selling technology to the Soviets. "Different responses are appropriate" now, Moyer said.